I've been plotting some large stipple files (i.e. 5000 to 10000 dots), but they always have cracks in them. At least it looks like a crack due to the incorrect position of some of the dots. These plots take anywhere from 45 mins to 1.5 hours to complete. They all look fins on the screen and I've wired with several different images all with similar results. I've also read the 'Improving precision' section of the wiki. The images are not full of these cracks, but there are always a few. Reducing the number of dots help, but that is most likely due to the loss of detail.